Study On The Fluid Flow And Heat Transfer In Abnormal Membrane Channels Used For Air Humidity Control

The traditional air humidity control technology is more and more difficult to meet the people’s increasing demand because of its high energy consumption or the liquid droplets entrained in processed air. Fortunately, the membrane system with membrane contactor as its core components used in air humidity control can easily meet the high requirements. Generally, there are two types of membrane in the contactor, the parallel plate membrane and the hollow fiber membrane. According to different arrangement of the membrane, it can form various types of flow channel. Considering the limitations of fabrication, installation and operation, the parallel plate membrane channel is always not a really rectangle but there is a concave or the shape of the channel is other form, and the fibers are randomly distributed in the hollow fiber membrane contactor while they are not distributed in the form of triangular or quadrilateral arrangement. In this paper, the fluid flow and heat transfer in abnormal membrane channels which including quadrilateral parallel-plate membrane channel with some deformation, hexagon parallel-plate membrane channel and elliptical hollow fiber membrane channel with random position and random angle distribution that used for air humidity control are studied with simulation and experimental opproaches. The characteristics of fluid flow and heat transfer will be analyzed.(1) In the quadrilateral parallel-plate membrane channel with some deformation, the characteristics of fluid flow and heat transfer were studied under different deformation and aspect ratio. The results show that in the air flow channel the larger the deformation heights Δh are, the greater the flow resistance is, and the higher the(fRe)m is. However the Num decreases with the aspect ratios b/a increasing under the same Δh in the air flow channel. The Num for LiCl solution is about 52.39%-60.15% larger than that for the water stream in the same channel.(2) For the hexagon parallel-plate membrane channel, different height and inlet length of the channels are studied. The results show that with increases on the flow channel height and Reynolds number, and the inlet length becomes smaller, the areas that the fluids stop or reflux will appear more easily. In the air flow channel, when the flow Reynolds number is less than 550, the smaller the height and inlet length of the channel are, the better the heat transfer. For water or desiccant solution, the greater the flow channel height and flow Reynolds number are, the better the heat transfer.(3) For the air flows across the elliptical hollow fiber membrane channel with random distribution, the random models have about 30.5%-89.8% larger mean friction factors fm than those with regular distribution, while the mean Nusselt numbers Num are about 5.5%-61.1% lower than those with regular distributions. Further, the fluid flow and heat transfer comprehensive capability of the random distribution is lower than that of regular one.(4) For the longitudinal transport phenomena of the air flows in the shell side between an elliptical hollow fiber membrane bundle with random position and random angle distribution, the elliptical semiaxis ratios b/a, random distributions in positions, and rotation angles have influences on the fluid flow and heat transfer. Among them, the random distribution in positions is the most important factor. The(fRe)C and NuC for the random model under various packing fractions are about 24.7%-65.4% and 19.5%-91.8% less than those for regular ones, respectively.The basic data is obtained by studying the fluid flow and heat transfer in abnormal membrane channels which can provide reference for future structural design and performance evaluation of the membrane contactor employed for air humidity control.